The present invention relates generally to voltage sensors for use with line conductors and, more particularly, to a compact capacitive divider-type sensor that is easy to manufacture and capable of measuring the potential of a medium-to-high voltage line conductor.
Capacitive divider-type sensors measure the AC voltage of a line conductor or bus bar. In such a device, a first capacitor (C1) with a known capacitance is connected to the line conductor. A second capacitor (C2) with a capacitance larger than the first is connected in series between C1 and ground. The voltage (VC2) across C2 is proportional to the line voltage (VL) between the line conductor and ground. Specifically, VL may be determined using the following equation:VC2=VL(C1/(C1+C2)).
When constructing a capacitive divider capable of measuring voltage in medium voltage (MV) to high voltage (HV) applications (e.g., approximately 1 kV to 50 kV), numerous design factors are typically taken into account. For example, both C1 and C2 are typically constructed using a number of individual capacitors to reduce the voltage on both C1 and C2 to a value that is within each capacitor's voltage rating. Such individual components, however, significantly increase complexity, inaccuracy possibilities, and manufacturing costs to the capacitive divider.
Also, the electric field (E-field) concentration on individual components of the capacitive divider influences the design of the capacitive divider. As is known, E-field concentration is, in part, a factor of the voltage of the line conductor. That is, as the voltage of the line conductor increases, E-field concentration on the individual components of the capacitive divider may increase as well. When E-field concentration is high, dielectric breakdown may occur between the line conductor and the voltage sensor. While E-field concentration may be minimized by increasing the distance between individual components of the capacitive divider, such an increase in component spacing also increases the overall size of the device.
It would therefore be desirable to design an apparatus and method for measuring the voltage of a medium-to-high voltage line conductor that is small, accurate, and relatively inexpensive to manufacture.